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Date Arithimetic in shell scripts

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# 1  
Old 05-29-2014
Date Arithimetic in shell scripts
Hi,

I have a file which has a date extension to it.
Like <filename>_01012014.

I need to rename the file as 12152013 , that is i need to be able to subtract 15 days from the date of the file name.

Please advise how this can be handled using shell scripting.

Regards,
VN
# 2  
Old 05-29-2014
Code:
$ cat tester
#!/bin/bash

file="filename_01012014"
touch $file
cp $file "${file%%_*}_"$(date -d"$(sed -r 's/(.{2})(.{2})(.{4})/\3\2\1/' <<<"${file##*_}") -15 days " +"%d%m%Y")

Code:
$ bash tester
$ ls filename_* -1
filename_01012014
filename_17122013

if happy replace cp with mv

for multiple files try this

Code:
#!/bin/bash

for file in filename_*; do
cp $file "${file%%_*}_"$(date -d"$(sed -r 's/(.{2})(.{2})(.{4})/\3\2\1/' <<<"${file##*_}") -15 days " +"%d%m%Y")
done

Tested with
Code:
GNU sed version 4.2.1
date (GNU coreutils) 8.13
GNU bash, version 4.2.25(1)-release (i686-pc-linux-gnu)

This User Gave Thanks to Akshay Hegde For This Post:
soliton
# 3  
Old 05-29-2014
I'm using korn shell.

sh tester
tester: syntax error at line 4: `(' unexpected

Please advise
# 4  
Old 05-29-2014
use ksh <scrptname>
# 5  
Old 05-29-2014
Thanks for your inputs.

ksh tester
tester[4]: syntax error at line 1 : `<' unexpected

I still get an error
# 6  
Old 05-29-2014
The problem appears to be GNU date. That is generally available on Linux servers, not other kinds of UNIX. What UNIX are you running the script on?
# 7  
Old 05-29-2014
Oracle Solaris and am using korn shell
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